ST. LOUIS (AP) — St. Louis police are investigating after someone spray-painted “KKK” on a road sign dedicating a stretch of Interstate 55 in honor of civil rights activist Rosa Parks.

Missouri Department of Transportation crews took down the two panels of the sign that were spray-painted after police completed an initial investigation. If the paint can’t be removed, the sign will be replaced.

Authorities say whoever is responsible could be charged with a hate crime.

Parks became an icon of the civil rights movement in 1955, when she refused to give up her seat on a bus in Montgomery, Ala.